The Collaborative International Dictionary of English v.0.48:

Piaster \Pi*as"ter\, n. [F. piastre, It. piastra a thin plate of
   metal, a dollar, LL. piastra, fr. L. emplastrum. See
   Plaster.]
   A silver coin of Spain and various other countries. See
   Peso. The Spanish piaster (commonly called peso, or peso
   duro) is of about the value of the American dollar. The
   Italian piaster, or scudo, was worth from 80 to 100 cents.
   The Turkish and Egyptian piasters are now worth about four
   and a half cents.
   [1913 Webster]

WordNet (r) 3.0 (2006):

piaster
    n 1: a fractional monetary unit in Egypt and Lebanon and Sudan
         and Syria [syn: piaster, piastre]
    2: 100 kurus equal 1 lira in Turkey [syn: kurus, piaster,
       piastre]